We propose to study the antigen or antigens induced by the Epstein-Barr virus on the surface of human B lymphocytes during the course of infectious mononucleosis. To do this we will obtain acute phase cells from infected individuals, separate human B cells and freeze them. After a period of time we will freshly bleed convalescent patients and determine the reactivity of their fresh T cells with their frozen B cells containing the antigen to the Epstein-Barr virus. Such studies are designed to determine whether the viral-induced antigen on the surface of the B cell is viral or host in nature, and whether or not it is restricted by a histocompatibility recognition antigen. More studies are contemplated with influenza virus both in acute infection and in laboratory inoculation of human cell lines.